Mri acoustic system, acoustic output device, and electro-acoustic transducer

ABSTRACT

A magnetic resonance imaging (MRI) acoustic system includes a magnet; an electro-acoustic transducer that includes a coil through which a current flows so that an attractive force or a repulsive force is generated with respect to the magnet, and a vibrating plate that vibrates in response to the attractive force or the repulsive force; and a controller that controls an intensity of a current input to the electro-acoustic transducer according to a position of the electro-acoustic transducer in a magnetic field generated by the magnet.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This application claims the priority from Korean Patent Application No.10-2012-0118671, filed on Oct. 24, 2012, in the Korean IntellectualProperty Office, the disclosure of which is incorporated herein in itsentirety by reference.

BACKGROUND

1. Field

Methods and apparatuses consistent with exemplary embodiments relate toa magnetic resonance imaging (MRI) acoustic system, and moreparticularly, to an MRI acoustic system including an acoustic outputdevice and an electro-acoustic transducer that operate based on amagnetic field of the MRI acoustic system.

2. Description of the Related Art

A magnetic resonance (MR) image is obtained through magnetic resonanceof an atomic nucleus in a magnetic field. Resonance of an atomic nucleusis a phenomenon where the atomic nucleus in a lower energy state changesto a higher energy state by absorbing high frequency energy whenspecific high frequency energy is irradiated to the atomic nucleus thatis in a magnetized state due to an external magnetic field. Atomicnucleuses have different resonance frequencies according to their types,and the resonance is affected by the intensity of the external magneticfield. There are a large number of atomic nucleuses in the human body,and generally, a hydrogen atomic nucleus is used for MRI.

An MRI apparatus is non-invasive, has a superior tissue contrastcompared to the computed tomography (CT), and generates no artifacts dueto bone structure. The MRI apparatus may take various cross-sectionalimages in desired directions without changing the position of a shootingobject. Thus, the MRI apparatus is widely used together with other imageimaging apparatuses.

A dynamic speaker, a loud speaker, or a piezo-electric speaker is usedas an electro-acoustic transducer for outputting an acoustic signal to apatient undergoing medical diagnosis by using the MRI apparatus.

A loud speaker or a piezo-electric speaker is mainly used as an acousticoutputting device for an MRI apparatus. However, a magnetic material inthe loud speaker may affect the magnetic field of the MRI apparatus, andthe piezo-electric speaker has a limited number of frequency bands forsound output and is expensive.

There is a need to develop an electro-acoustic transducer and anacoustic output device with the decreased production cost, improvedsound quality, consistent low sound generation ability, and lesseneddegree of effect on the quality of an MRI image.

SUMMARY

Exemplary embodiments may address at least the above problems and/ordisadvantages and other disadvantages not described above. Also, theexemplary embodiments are not required to overcome the disadvantagesdescribed above, and an exemplary embodiment may not overcome any of theproblems described above.

According to an aspect of an exemplary embodiment, there is provided anMRI acoustic system including: an MRI apparatus that includes a magnet;an electro-acoustic transducer that includes a coil through which acurrent flows so that an attractive force or a repulsive force isgenerated with respect to the magnet and a vibrating plate that iscombined with the coil and vibrates in response to the attractive forceor the repulsive force; and a controller that controls the intensity ofa current input to the electro-acoustic transducer according to ahorizontal position of the electro-acoustic transducer in a magneticfield generated by the magnet.

The MRI acoustic system may further include a storage that stores inadvance an intensity of the current according to the horizontal positionof the electro-acoustic transducer, the controller controlling theintensity of the current so that the vibrating plate vibrates regardlessof an intensity of the magnetic field according to a change of thehorizontal position of the electro-acoustic transducer.

The MRI acoustic system may further include a detector that detects anintensity of the magnetic field, the controller blocking the currentinput to the electro-acoustic transducer when the intensity of themagnetic field is detected to be below a critical value.

The controller may block the current input to the electro-acoustictransducer when the horizontal position of the electro-acoustictransducer is outside a predetermined range.

The MRI acoustic system may further include a filter that preventsinterference between radio-frequency (RF) signals generated from the MRIapparatus and the electro-acoustic transducer.

The electro-acoustic transducer may be disposed so that a vibratingdirection of the vibrating plate and a direction of a magnetic fluxfocused by the magnet are not perpendicular to each other.

The electro-acoustic transducer may be positioned in the magnetic fieldformed by the magnet so that a central axis of the coil and a directionof a magnetic flux focused by the magnet are not perpendicular to eachother.

The electro-acoustic transducer may be positioned on a head portion of acradle where the patient is located to move in the magnetic field.

The controller may control an intensity of the current according to amoving distance of the cradle into the magnetic field of the MRIapparatus, the electro-acoustic transducer is being positioned on thecradle.

The electro-acoustic transducer may be mounted on a head RF coil of theMRI apparatus.

The electro-acoustic transducer may be mounted on a headset or anearphone of the MRI apparatus.

The MRI acoustic system may further include a detector that detects theintensity of the magnetic field, the controller controlling theintensity of the current according to the intensity of the detectedmagnetic field.

According to an aspect of an exemplary embodiment, there is provided anacoustic output device that uses a magnetic field of the MRI apparatus,including: a coil through which a current for generating an attractiveforce or a repulsive force with respect to a magnet of the MRI apparatusflows; a vibrating plate that is combined with the coil and vibratesaccording to the attractive force or the repulsive force; and acontroller that controls an intensity of an input current that flowsthrough the coil in the magnetic field according to a horizontalposition of the electro-acoustic transducer.

The acoustic output device may further include a storage that stores inadvance an intensity of the input current according to the horizontalposition of the electro-acoustic transducer, the controller controllingthe intensity of the input current so that the vibrating plate vibratesregardless of the intensity of the magnetic field according to thehorizontal position of the electro-acoustic transducer.

The acoustic output device may further include a detector that detectsthe intensity of the magnetic field, the controller blocking the currentinput to the electro-acoustic transducer when the intensity of themagnetic field is detected to be below a critical value.

The controller may block the current input to the electro-acoustictransducer when the horizontal position of the electro-acoustictransducer is outside a predetermined range.

The acoustic output device may further include a headset or an earphone.

According to an aspect of an exemplary embodiment, there is provided anelectro-acoustic transducer that uses a magnetic field of an MRIapparatus, including: a first coil through which a current forgenerating an attractive force or a repulsive force with respect to theMRI apparatus flows; a second coil for reducing a magnetic fieldgenerated by the current that flows in the first coil; and a vibratingplate that is combined with the first coil and vibrates according to theattractive force or the repulsive force.

A current having a predetermined intensity may flow through the secondcoil to reduce the magnetic field generated by the first coil.

The second coil may be wound by a predetermined number of turns forreducing the magnetic field generated by the first coil.

The electro-acoustic transducer may further include a fixing unit thatfixes the second coil, wherein the second coil has a concentric axiswith the first coil and is combined with the fixing unit on an innerside or outer side of the first coil.

The direction of a current that flows through the second coil may beopposite to the direction of a current that flows through the firstcoil.

The electro-acoustic transducer may be positioned on a head portion of acradle where the patient is located in the MRI apparatus.

The electro-acoustic transducer may be mounted on a head RF coil of theMRI apparatus.

The electro-acoustic transducer may be mounted on a headset or anearphone of the MRI apparatus.

According to an aspect of an exemplary embodiment, there is provided anacoustic system that includes the electro-acoustic transducer describedabove.

According to an aspect of an exemplary embodiment, there is provided anelectro-acoustic transducer that uses a magnetic field of an MRIapparatus, including: a vibrating unit that vibrates according to aLorentz force generated by the magnetic field; a supporting unit thatfixes both edges of the vibrating unit; and a first coil that isdisposed on the vibrating unit and vibrates together with the vibratingunit.

The electro-acoustic transducer may further include a second coil thatis fixed on the supporting unit and is combined with the first coil.

The electro-acoustic transducer may include at least one first coil andat least one second coil, wherein the at least one first coil and the atleast one second coil are combined with each other and are disposedalong at least one surface of the supporting unit and the vibratingunit.

The first coil and the second coil may be parallel to each other, andcurrents respectively flow therethrough in opposite directions.

The first coil may include a thin film coil formed on the vibratingunit.

The vibrating unit may include a first vibrating unit and a secondvibrating unit disposed in parallel to the first vibrating unit, bothedges of the first vibrating unit and both edges of the second vibratingunit being respectively combined with the supporting unit, and the firstcoil being disposed on the first and second vibrating units.

The first coil may be disposed on the vibrating unit in at least onerepeating pattern.

The first coils may be disposed so that a location of the center of therepeating pattern is biased on a side of the first coils.

The vibrating unit may include a vibrating plate that vibrates due tothe Lorentz force and is separated from the supporting unit, and aconnection unit that connects the vibrating plate to the supportingunit, wherein the first coil is disposed on the vibrating plate.

The vibrating unit may include a vibrating film that vibrates due to theLorentz force.

The vibrating unit may include a vibrating plate that vibrates due tothe Lorentz force and is formed of an elastic member.

The electro-acoustic transducer may be positioned on a head portion of acradle where the patient is positioned in the MRI apparatus.

The electro-acoustic transducer may be mounted on a head RF coil of theMRI apparatus.

The electro-acoustic transducer may be mounted on a headset or anearphone of the MRI apparatus.

According to an aspect of an exemplary embodiment, there is provided anelectro-acoustic transducer that uses a magnetic field of an MRIapparatus, including: a vibrating unit that vibrates according to anattractive force or a repulsive force with respect to a magnet of theMRI apparatus; a first coil that is disposed on the vibrating unit in atleast one repeating pattern and through which a current for generatingthe attractive force or the repulsive force flows; and a second coilthat is combined with the first coil, and through which a current inputto the first coil and a current output from the first coil flows.

The pattern may include a screw shape pattern.

The pattern may include a rectangular shape pattern.

The patterns may be formed by consecutively disposing the first coilsalong a predetermined direction on the vibrating unit.

The second coil may be disposed on a lower surface of the vibratingunit.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and/or other aspects will become more apparent by describingcertain exemplary embodiments with reference to the accompanyingdrawings, in which:

FIGS. 1A and 1B are drawings to illustrate and explain operation of arelated art electro-acoustic transducers of an MRI system;

FIG. 2 illustrates an MRI acoustic system according to an exemplaryembodiment;

FIG. 3 is a block diagram showing a configuration of an MRI acousticsystem according to an exemplary embodiment;

FIGS. 4A, 4B, 4C, and 4D show positioning of an electro-acoustictransducer according to an exemplary embodiment;

FIGS. 5A and 5B are perspective views of an electro-acoustic transducerand an MRI apparatus according to an exemplary embodiment;

FIGS. 6A, 6B, 6C, and 6D show control of intensity of an input currentaccording to horizontal positions of a cradle;

FIGS. 7A and 7B show a headset according to an exemplary embodiment;

FIGS. 8A, 8B, and 8C show positioning of an electro-acoustic transduceraccording to an exemplary embodiment;

FIGS. 9A and 9B show a structure of an electro-acoustic transduceraccording to an exemplary embodiment;

FIGS. 10A and 10B show a structure of an electro-acoustic transduceraccording to an exemplary embodiment;

FIG. 11 is a perspective view showing a structure of an electro-acoustictransducer according to an exemplary embodiment;

FIGS. 12A and 12B show a structure of an electro-acoustic transduceraccording to an exemplary embodiment;

FIG. 13 is a perspective view showing a structure of an electro-acoustictransducer according to an exemplary embodiment;

FIG. 14 is a perspective view showing a structure of an electro-acoustictransducer according to an exemplary embodiment;

FIGS. 15A and 15B show a structure of an electro-acoustic transduceraccording to an exemplary embodiment;

FIGS. 16A and 16B show positioning of an electro-acoustic transduceraccording to an exemplary embodiment;

FIG. 17 is a drawing showing mounting of an electro-acoustic transducerin an acoustic output device according to an exemplary embodiment;

FIGS. 18A and 18B show positioning of an electro-acoustic transduceraccording to an exemplary embodiment; and

FIGS. 19A, 19B, and 19C show patterns of an electro-acoustic transduceraccording to an exemplary embodiment.

DETAILED DESCRIPTION

Below, certain exemplary embodiments are described in greater detailwith reference to the accompanying drawings.

In the following description, like reference numerals are used for thelike elements, even in different drawings. The matters defined in thedescription, such as detailed construction and elements, are provided toassist in a comprehensive understanding of exemplary embodiments.However, exemplary embodiments can be carried out without thosespecifically defined matters. Also, well-known functions orconstructions are not described in detail since that would obscure thedescription with unnecessary detail.

The terms used herein may vary according to the intention of one ofordinary skill in the art, the precedent, or the emergence of newtechnologies. It should be understood that “comprises,” “comprising,”“includes,” and/or “including” means an inclusion of other additionalelements.

FIG. 1 is a drawing illustrating a related art electro-acoustictransducer of an MRI system.

FIG. 1A is a perspective view showing an MRI apparatus 10 having adynamic speaker 11. The dynamic speaker 11 is an acoustic output deviceof the MRI system. The dynamic speaker 11 has a high acousticperformance, but includes a magnetic body such as an iron or a permanentmagnet.

Accordingly, the dynamic speaker 11 is positioned at a location far froma bore of the MRI apparatus in order to minimize its effect on amagnetic field of the MRI system. For example, the dynamic speaker 11 ispositioned at the outside or an edge portion 12 of a cradle where anobject to be diagnosed is located, and a sound output from the dynamicspeaker 11 is transmitted to an object through an acoustic path providedin the cradle. Accordingly, the sound of the dynamic speaker 11 may bedistorted due to the long transmission path and includes noise.

FIG. 1B shows a graph 20 of an acoustic characteristic of apiezo-electric speaker of the MRI system. The piezo-electric speaker isformed of a piezo-electric ceramic, which is a non-magnetic materialthat contracts/expands in response to an input electric signal, andthus, is installed inside a bore since it does not nearly affect amagnetic field of the MRI apparatus.

However, as depicted in graph 20, generally, a resonance frequency f0 ofthe piezo-electric speaker is greater than 1 kHz, which is greater thanthat of the dynamic speaker 11. Accordingly, due to the difficulties togenerate a low sound and the difficulties to make a wide-width electrodeof the piezo-electric speaker, it is difficult to transmit an RF signalof the MRI apparatus to a speaker, and thus, a distortion of an MRIimage may occur. Also, the piezo-electric speaker that includes apiezo-electric ceramic, which is a non-magnetic material, has aproduction cost higher than that of the dynamic speaker 11.

FIG. 2 illustrates an MRI acoustic system 100 according to an exemplaryembodiment. The MRI acoustic system 100 may include an MRI apparatus110, an electro-acoustic transducer 120, and a controller 130. The MRIacoustic system 100 may further include other elements besides theelements depicted in FIG. 2.

The MRI apparatus 110 is used to diagnose a patient 113 positioned on acradle 112 by using a magnetic field generated from a magnet. The MRIapparatus 110 generates an MRI image of the patient 113 by processing amagnetic resonance signal received from the patient 113 placed in themagnetic field, and may display an MRI image on a screen.

The MRI apparatus 110 includes a superconducting magnet or a permanentmagnet as an element for generating a magnetic field. In the case of thesuperconducting magnet, liquid helium may be used as refrigerant. Also,with respect to the superconducting magnet, liquid nitrogen or aconduction cooling method may be used besides the liquid helium. The MRIapparatus 110 may be located in a room shielded from external RF signalsby being separated from an operating room where a radiologist controlsthe operation of the MRI apparatus 110.

The electro-acoustic transducer 120 generates an acoustic signal via themagnetic field of the MRI apparatus 110. The acoustic signal generatedfrom the electro-acoustic transducer 120 is transmitted to a user, andthe electro-acoustic transducer 120 may transmit a signal from the userof the MRI apparatus 110 to the patient 113. Hereinafter, the “acousticsignal” denotes a sound wave generated by vibration of a vibrating plateof the electro-acoustic transducer 120. However, the “acoustic signal”is not limited thereto, and may denote any predetermined signalelectrically generated.

The electro-acoustic transducer 120 may include a coil through which acurrent flows for generating an attractive force or a repulsive forcewith respect to a magnet of the MRI apparatus 110, and a vibrating platethat is combined to the coil to vibrate according to the attractiveforce or repulsive force. A configuration of the electro-acoustictransducer 120 and an operation of generating an acoustic signal byvibrating are described with reference to FIG. 4.

Furthermore, according to an exemplary embodiment, the electro-acoustictransducer 120 may include a non-magnetic vibration film instead of thevibrating plate, which vibrates according to a force that interacts withthe magnetic field of the MRI apparatus 110. This embodiment will bedescribed with reference to FIGS. 11 through 13.

The electro-acoustic transducer 120 according to an exemplary embodimentmay be located at least one of outside a bore 111 and inside the bore111. The electro-acoustic transducer 120 according to an exemplaryembodiment generates an acoustic signal via the magnetic field of themagnet of the MRI apparatus 110 instead of a magnetic material of adynamic speaker. Accordingly, since the electro-acoustic transducer 120does not affect the magnetic field of the MRI apparatus 110, theelectro-acoustic transducer 120 may be located in the bore 111.

The controller 130 controls an intensity of a current input to theelectro-acoustic transducer 120 according to a horizontal position ofthe electro-acoustic transducer 120. That is, the controller 130 maycontrol the intensity of the current input to the electro-acoustictransducer 120 to generate an acoustic signal according to thehorizontal position of the electro-acoustic transducer 120 on the MRIapparatus 110. The “horizontal position” may denote a position in ahorizontal direction of the electro-acoustic transducer 120, i.e., adirection substantially parallel to a movement of the cradle 112 in thebore 111 of the MRI apparatus 110. Accordingly, the horizontal positionmay be changed according to the movement of the cradle 112 in the bore111 or according to the position change of the patient 113 on the cradle112.

More specifically, the patient 113 is positioned on the cradle 112, andthe cradle 112 moves into the bore 111 of the MRI apparatus 110 tocontrol a position of the patient 113. That is, as depicted in FIG. 2,the cradle 112 may move in the magnetic field to image an region ofinterest (ROI), for example, knee, neck, waist, etc., of the patient113, in a horizontal direction 98, toward the end portion 94 of the bore111 or away from the end portion 94 of the bore 111.

As described above, the electro-acoustic transducer 120 is driven by anattractive force or a repulsive force between the magnetic fieldgenerated by an input current and the magnet of the MRI apparatus 110.That is, when an intensity of the current input to the electro-acoustictransducer 120 increases, the intensity of the magnetic field generatedby the electro-acoustic transducer 120 is increased, and thus, theintensity of a force interacting with the magnet of the MRI apparatus110 is changed. Accordingly, the intensity of the input current isrelated to the intensity of an acoustic signal generated by theelectro-acoustic transducer 120. As the intensity of input currentincreases, the intensity of an acoustic signal also increases.

The controller 130 controls the intensity of a current input(hereinafter, input current) to the electro-acoustic transducer 120according to the horizontal position of the electro-acoustic transducer120 in the magnetic field, and thus, the intensity of the acousticsignal generated by the electro-acoustic transducer 120 may becontrolled. The current exemplary embodiment is described below indetail with reference to FIG. 6.

As described with reference to FIG. 1, the dynamic speaker of a relatedart MRI acoustic system 100 is located away from the bore since thedynamic speaker may affect the magnetic field of the MRI apparatus.Accordingly, if the patient is positioned away from the dynamic speaker,the length of a transmission path of the acoustic signal is increased,and thus, the degree of distortion of the acoustic signal is increased.

However, according to the MRI acoustic system 100 depicted in FIG. 2,the electro-acoustic transducer 120 does not affect the magnetic fieldof the MRI apparatus 110, and in the MRI apparatus 110, the intensity ofthe acoustic signal generated by the electro-acoustic transducer 120 iscontrolled according to the horizontal position of the cradle 112.Accordingly, regardless of the position of the patient within the bore111, an acoustic signal with constant intensity may be transmitted tothe patient 113.

The electro-acoustic transducer 120 depicted in FIG. 2 may be mounted onan acoustic output device 126. For example, the electro-acoustictransducer 120 may be provided on various acoustic output devices 126such as a headset or an earphone. According to an exemplary embodiment,the electro-acoustic transducer 120 may also be provided on a head RFcoil of the MRI apparatus 110 or on a head portion 96 of the cradle 112where the patient 113 is positioned.

FIG. 3 is a block diagram showing a configuration of the MRI acousticsystem 100 according to an exemplary embodiment. The MRI acoustic system100 of FIG. 3 includes a signal processor 125 that includes a storage131, a detector 132, and a filter 133 in addition to the MRI apparatus110, the electro-acoustic transducer 120, and the controller 130described with reference to FIG. 2. Descriptions of the MRI apparatus110, the electro-acoustic transducer 120, and the controller 130 madewith reference to FIG. 2 will not be repeated.

As depicted in FIG. 3, the controller 130 may include a horizontalposition detector 138 and a current controller 139. Hereinafter, inaddition to the description about the controller 130 of FIG. 2, thehorizontal position detector 138 and the current controller 139 depictedin FIG. 3 will be described.

The horizontal position detector 138 detects a horizontal position ofthe electro-acoustic transducer 120, that is, detects how far theelectro-acoustic transducer 120 is moved into the bore 111 of the MRIapparatus 110. That is, the horizontal position detector 138 may detecta horizontal position of the electro-acoustic transducer 120 that ismoved in response to an electrical signal (when a radiologist controlsthe MRI apparatus 110 in an operating room) or by a physical method(when the radiologist directly moves the cradle 112 before imagingstarts). The horizontal position detector 138 may transmit informationregarding the horizontal position of the electro-acoustic transducer 120to the current controller 139.

Meanwhile, the horizontal position of the electro-acoustic transducer120 may be changed according to the movement of the cradle 112 into theMRI apparatus 110. That is, according to the movement of the cradle 112on which the patient 113 is positioned, the horizontal position in themagnetic field of the electro-acoustic transducer 120 worn by thepatient 113 or provided in the cradle 112 may be changed.

For example, when the cradle 112 is moved into the bore 111 by anexternal electrical signal, the horizontal position detector 138 mayelectrically detect information regarding the horizontal position of theelectro-acoustic transducer 120 by fetching the external signal thatmoves the cradle 112. That is, the horizontal position detector 138 maydetect a horizontal position of the electro-acoustic transducer 120 thatvaries according to the movement of the cradle 112 into the magneticfield.

The horizontal position detector 138 may detect the position of thecradle 112 by using at least one sensor provided on a table thatsupports and moves the cradle 112. For example, the horizontal positiondetector 138 may detect a horizontal position of the electro-acoustictransducer 120 according to the movement of the cradle 112 through thesensors disposed with predetermined gaps.

Furthermore, the horizontal position detector 138 may detect ahorizontal position of the electro-acoustic transducer 120 by anexternal input signal. That is, when a user of the MRI apparatus 110controls a horizontal position of the electro-acoustic transducer 120before moving the patient 113 into the bore 111, the user may manuallyinput a horizontal position. Afterwards, the horizontal positiondetector 138 may detect a horizontal position of the electro-acoustictransducer 120 by obtaining information of position that is directlyinput by the user.

According to an embodiment of the current invention, the horizontalposition detector 138 may detect a horizontal position of theelectro-acoustic transducer 120 according to an intensity of a magneticfield that is detected by a detector 132 at a predetermined location.

The current controller 139 controls an intensity of a current input tothe electro-acoustic transducer 120. That is, a current flows through acoil of the electro-acoustic transducer 120 so that an attractive forceor a repulsive force, which is a force interacting with a magnet of theMRI apparatus 110, is generated, and thus, the current controller 139may control the intensity of the current that is input to the coil. Aforce that vibrates the electro-acoustic transducer 120 increasesproportional to the intensity of the input current. Therefore, thecurrent controller 139 may control the intensity of an acoustic signalthat is generated by the electro-acoustic transducer 120 by controllingthe intensity of the input current.

The current controller 139 may block the input current. That is, if acurrent flows through the coil when the electro-acoustic transducer 120does not need to generate an acoustic signal, an unnecessary burden mayoccur on the electro-acoustic transducer 120, and thus, the lifetime ofthe electro-acoustic transducer 120 may be reduced. According to anexemplary embodiment, the current controller 139 may block an inputcurrent being input to the electro-acoustic transducer 120 when theintensity of the magnetic field is detected to be below a critical valueor when the cradle 112 is positioned outside the predeterminedhorizontal position (that is, when there is no need to transmit a soundto the patient 113). The current embodiment is described below in detailwith reference to FIG. 6.

Hereinafter, various elements connected to the controller 130 forcontrolling a current input to the electro-acoustic transducer 120 willbe described.

The signal processor 125 is connected to the MRI apparatus 110 and theelectro-acoustic transducer 120 and generates a control signal forcontrolling at least one of the MRI apparatus 110 and theelectro-acoustic transducer 120, and controls an operation of at leastone of the MRI apparatus 110 and the electro-acoustic transducer 120 bytransmitting the generated control signal.

The signal processor 125, as described with reference to FIGS. 2 and 3,may include the controller 130 that controls a current input to theelectro-acoustic transducer 120 according to the horizontal position ofthe cradle 112 of the MRI apparatus 110. The signal processor 125 mayinclude the storage 131, the detector 132, and the filter 133 inaddition to the controller 130, and may further include other elementsbesides the elements depicted in FIG. 3.

The storage 131 stores various kinds of information for controlling theelectro-acoustic transducer 120 or the MRI apparatus 110. For example,the storage 131 may store information regarding the intensity ofmagnetic field of the MRI apparatus 110, information with regard to adirection of a magnetic flux, and information regarding physicalcharacteristics of the coil and the vibrating plate of theelectro-acoustic transducer 120.

According to an exemplary embodiment, the storage 131 may storeinformation with regard to the intensity of input current according to ahorizontal position of the electro-acoustic transducer 120. That is, inan exemplary embodiment, the controller 130 may use information storedin the storage 131 to control the intensity of the input current.

More specifically, the intensity of the magnetic field of the MRIapparatus 110 varies according to the position where the magnetic fieldis measured in and out of the bore 111 (this will be more specificallydescribed with reference to FIG. 6). Accordingly, the intensity of themagnetic field that affects the electro-acoustic transducer 120 variesaccording to a position where the electro-acoustic transducer 120 ispositioned in the bore 111. As a result, the intensity of an acousticsignal generated by the electro-acoustic transducer 120 is changed. Thechange of the intensity may lead to a problem in that a constantintensity acoustic signal may be difficult to transmit to the user.

Accordingly, the storage 131 may store information regarding theintensity of the magnetic field that varies at an arbitrary position inthe magnetic field, and may store in advance information regarding theintensity of an input current that is required for the electro-acoustictransducer 120 to generate a constant intensity acoustic signalregardless of the intensity variation (that is, the variation of thehorizontal position) of the magnetic field

When information that the cradle 112 has moved to a predeterminedposition in the bore 111 is obtained by the horizontal position detector138, the controller 130 controls the current controller 139 by using theinformation of the horizontal position and the intensity of an inputcurrent, which are stored in the storage 131 in advance. That is, thestorage 131 may store in advance information for providing a constantacoustic signal to the user although the intensity of the magnetic fieldvaries according to the position change of the electro-acoustictransducer 120.

The storage 131 may store information about the intensity of the inputcurrent according to the horizontal position in a table or a list. Forexample, after dividing the horizontal position where theelectro-acoustic transducer 120 may be able to move into a plurality ofsections, the storage 131 may store the intensity of the input currentby matching the intensity with each of the sections. Also, after storinga relational expression between the horizontal position of theelectro-acoustic transducer 120 and the intensity of the current, whenthe horizontal position of the electro-acoustic transducer 120 is inputfrom the horizontal position detector 138, the storage 131 may transmitthe intensity of the input current to the current controller 139 byusing the stored relational expression.

The detector 132 detects the intensity the magnetic field of the MRIapparatus 110. The detector 132 may detect the intensity of the magneticfield at predetermined positions inside or outside the bore 111. Inother words, the detector 132 may detect the intensity of the magneticfield at a predetermined position inside the magnetic field according tothe movement of the horizontal position of the electro-acoustictransducer 120. For example, the detector 132 may detect the intensityof the magnetic field at a head portion 96 of the cradle 112 (that is,at a predetermined position where the head of the patient 113 ispositioned) on which the patient 113 is positioned.

The detector 132 may transmit information regarding the intensity of thedetected magnetic field to the current controller 139, and as describedabove, the current controller 139 may block the current input to theelectro-acoustic transducer 120 when the intensity of the magnetic fieldis detected to be below a critical value.

The detector 132 may detect the intensity of the magnetic field invarious ways. For example, when the storage 131 stores in advanceinformation regarding the intensity of the magnetic field according tothe horizontal position of the electro-acoustic transducer 120, thedetector 132 may obtain the intensity regarding the magnetic field fromthe storage 131. The detector 132 may detect a magnetic resonancephenomenon by an electromagnetic induction method or a magneticresonance phenomenon may be measured via an intensity of light byoptically pumping a low pressure steam of an alkali metal.

The detector 132 may obtain the intensity regarding the magnetic fieldby using data stored in advance in the storage 131, besides directlymeasuring the intensity of the magnetic field. That is, when the storage131 stores a value of the intensity of the magnetic field in advanceaccording to the horizontal position of the electro-acoustic transducer120, the detector 132 may obtain information about the intensity of themagnetic field according to the moving distance of the electro-acoustictransducer 120 in the horizontal direction from the stored data.

The filter 133 prevents interference between an RF signal of the MRIapparatus 110 and the electro-acoustic transducer 120. That is, thefilter 133 prevents occurrence of an interference phenomenon between aresonance frequency of the electro-acoustic transducer 120 and thefrequency of the RF signal of the MRI apparatus 110. The filter 133 maybe electrically connected to the coil of the electro-acoustic transducer120, and may include an RLC circuit or an RC circuit. The filter 133 mayprotect the electro-acoustic transducer 120 and the signal processor 125from an effect due to variation of a magnetic field that is generated ina gradient coil and an RF signal generated in an RF coil.

The signal processor 125 may control various processes for outputting asound to the patient 113 by being connected via a wire or in a wirelessmanner to the electro-acoustic transducer 120.

As shown in FIG. 3, the acoustic output device 126 includes theelectro-acoustic transducer 120 and the signal processor 125. That is,the acoustic output device 126 according to an exemplary embodimentincludes the electro-acoustic transducer 120 that generates an acousticsignal and the signal processor 125 that controls the current input tothe electro-acoustic transducer 120.

The acoustic output device 126 may be configured in various ways togenerate an acoustic signal and transmit the same to the patient 113.According to an exemplary embodiment, the acoustic output device 126 mayinclude a headset or an earphone.

The signal processor 125 may be a separate element placed outside theacoustic output device 126. According to an exemplary embodiment, thesignal processor 125 may be an external mounting device placed at apredetermined distance from the acoustic output device 126, and may beconnected to the acoustic output device 126 via a wire or in a wirelessmanner.

FIGS. 4A, 4B, 4C, and 4D show positioning of an electro-acoustictransducer according to an exemplary embodiment.

FIG. 4A is a drawing for explaining a solenoid coil and the Ampere'sRule. As depicted in FIG. 4A, when a current flows through the solenoidcoil, a magnetic field is formed around the solenoid coil, and adirection of a magnet flux is in a direction of the central axis of thesolenoid coil (in a direction according to the Ampere's Rule (theright-hand screw rule)). The solenoid coil may be regarded as a magnetthat generates the magnetic field by a current that flows therethrough.

FIG. 4B shows the electro-acoustic transducer 120 that uses a magneticfield of the magnet of the MRI apparatus 110 by being located in thebore 111. In FIG. 4B, the magnetic field generated by the magnet of theMRI apparatus 110 is shown by arrows 30. FIG. 4B shows an ideal magnethaving a sufficient length. Accordingly, in FIG. 4B, the magnetic fieldin the bore 111 is uniform. However, actually, the magnetic field maynot be completely uniform at each position in the bore 111.

In FIG. 4B, if the coil of the electro-acoustic transducer 120 is asolenoid coil, a magnetic field is generated in a central axis directionof the electro-acoustic transducer 120 when a current flows through thecoil. The direction of the magnetic field generated by the coil of theelectro-acoustic transducer 120 varies according to the direction of thecurrent that flows through the coil. The electro-acoustic transducer 120may be regarded as a magnet that generates a magnetic field according toa current that flows through a coil within a region where the magneticfield is distributed. Thus, as long as a magnetic field generated by themagnet of the MRI apparatus 110 reaches the electro-acoustic transducer120, the electro-acoustic transducer 120 may operate by being positionedin the vicinity of the magnet.

Accordingly, an attractive force or a repulsive force is generatedbetween the electro-acoustic transducer 120 and the magnet according tothe direction of a current that flows through the coil. That is, when acurrent flows through the coil, the electro-acoustic transducer 120generates a force that is interacting with the magnet of the bore 111according to the direction of a current that flows through the coil andthe electro-acoustic transducer 120 vibrates.

FIGS. 4C and 4D are drawings showing the position and direction of theelectro-acoustic transducer 120 in the bore 111, according to anexemplary embodiment. In FIGS. 4C and 4D, the electro-acoustictransducer 120 includes a coil 122 through which a current flows and avibrating plate 121 that vibrates according to a force that isinteracting with a magnet of the bore 111.

According to FIG. 4C, the electro-acoustic transducer 120 may bepositioned so that the vibration direction 28, i.e., in left and rightdirections in FIG. 4C, of the vibrating plate 121 and the direction 30of a magnetic flux are parallel to each other. That is, theelectro-acoustic transducer 120 may be positioned so that the directionof a magnetic field generated by a current that flows through the coil122 and the direction of a magnetic field generated by a magnet areparallel to each other.

Although a described-above acoustic signal is generated when thevibration direction of the electro-acoustic transducer 120 and thedirection of the magnetic field generated by the magnet of the MRIapparatus 110 are parallel to each other, the two directions are notlimited to being parallel to each other. In other words, as long as thetwo directions described above are not perpendicular to each other, theelectro-acoustic transducer 120 may generate an acoustic signal byvibrating due to a force interacting with the magnet. That is, theelectro-acoustic transducer 120 may be positioned so that the vibratingdirection thereof is not perpendicular to the direction of the magneticfield.

According to FIG. 4D, the electro-acoustic transducer 120 may bepositioned so that a central axis 123 that is formed by the coil 122 andthe direction 30 in which a magnet flux is focused are parallel to eachother. That is, the electro-acoustic transducer 120 may be positioned sothat the direction of a magnetic field generated by a current that flowsthrough the coil 122 and the direction of a magnetic field of the magnetare parallel to each other. However, an exemplary embodiment is notlimited to the case where the direction of a magnetic field of theelectro-acoustic transducer 120 and the direction of a magnetic field ofthe magnet of the MRI apparatus 110 are parallel to each other. That is,the electro-acoustic transducer 120 may generate an acoustic signal bybeing positioned so that the direction of the magnetic field of theelectro-acoustic transducer 120 and the direction of a magnetic field ofthe magnet of the MRI apparatus 110 are not perpendicular to each other.

As described with reference to FIG. 4, the electro-acoustic transducer120 may vibrate according to a force that is interacting with the magnetof the MRI apparatus 110 by being positioned in the bore 111, therebygenerating an acoustic signal. In FIG. 4, the case where theelectro-acoustic transducer 120 is positioned in the bore 111 isdescribed. However, the above description may be the same when theelectro-acoustic transducer 120 is positioned outside the bore 111 andthe magnetic field of the MRI magnet is distributed.

That is, when the electro-acoustic transducer 120 is positioned outsidethe bore 111, an attractive force or a repulsive force is generatedbetween the electro-acoustic transducer 120 and the magnet of the MRIapparatus 110, and the vibrating plate 121 vibrates according to aninteracting force. In other words, although the intensity of theinteracting force may vary, the vibrating plate 121 may still vibrate.

FIGS. 5A and 5B are perspective views of the electro-acoustic transducer120 and the MRI apparatus 110 according to an exemplary embodiment. InFIG. 5A, the magnet of the MRI apparatus 110 is a superconductingmagnet, and in FIG. 5B, the magnet of the MRI apparatus 110 is apermanent magnet. The magnet of FIG. 5B may be of an open type.

According to FIG. 5A, the electro-acoustic transducer 120 may bepositioned outside or inside the bore 111, as described with referenceto FIG. 4, and thus, the repeated description will be omitted. Theelectro-acoustic transducer 120 in FIG. 5B may be positioned within agantry of the MRI apparatus 110. That is, in a permanent magnet MRIapparatus 110 that are also referred to as an open type MRI apparatus,the electro-acoustic transducer 120 may be positioned in a magneticfield formed by an upper magnet 151 and a lower magnet 152.

The electro-acoustic transducer 120 in FIG. 5B may be positioned so thatthe vibration direction 26, i.e., the up and down direction in FIG. 5B,of the vibrating plate 121 is parallel to the direction 30 of a magnetflux formed by the upper magnet 151 and the lower magnet 152. Theelectro-acoustic transducer 120 may be positioned so that the centralaxis 123 of the coil 122 is parallel to the direction of a magnet fluxformed by the upper magnet 151 and the lower magnet 152. Accordingly,the electro-acoustic transducer 120 FIG. 5B generates an acoustic signalby vibrating vertically in the direction of a magnet flux. Theelectro-acoustic transducer 120 in FIG. 5A may be positioned so that thedirection of a magnet flux is not perpendicular to the vibrationdirection.

FIGS. 6A, 6B, 6C, and 6D show control of an intensity of a current inputto the electro-acoustic transducer 120 according to the horizontalposition of the electro-acoustic transducer 120, according to anexemplary embodiment.

FIG. 6A shows the intensities of a magnetic field inside and outside thebore 111. FIGS. 6B through 6D show movements of the cradle 112 when theelectro-acoustic transducer 120 is provided on a headset.

More specifically, in FIG. 6B, the head of the patient 113 is positionedat a center portion 620 of the bore 111, in FIG. 6C, the waist of thepatient 113 is positioned at the center portion 620 of the bore 111, andin FIG. 6D, the knees of the patient 113 are positioned at the centerportion 620 of the bore 111. That is, in drawings FIGS. 6B through 6D,the horizontal position of the cradle 112 is controlled so that the ROIof the patient 113 is positioned at the center portion 620 of the bore111.

Hereinafter, the control of the intensity of a current input to theelectro-acoustic transducer 120 according to the horizontal position ofthe electro-acoustic transducer 120 as depicted in FIGS. 6B through 6Daccording to an exemplary embodiment will be described.

In FIG. 6A, the intensity of a magnetic field generated by a magnet ofthe bore 111 varies according to positions inside and outside the bore111. A graph 610 depicted in FIG. 6A shows the variations of theintensity of the magnetic field. In FIG. 6A, when moving in a right-handdirection from an entrance 618 of the bore 111, first, a region 111 b isa region where the magnet flux is most densely focused (that is, themagnetic intensity is the strongest in this region). Also, a magneticfield having a relatively uniform intensity is formed in the region 111b.

Next, the intensity of the magnetic field is reduced when moving fromthe region 111 b towards a region 111 c in the bore 111. That is, unlikea theoretical magnet, a real magnet has a fixed length. Therefore, theintensity of the magnetic field in the bore 111 is weaker near the endof the bore 111. However, as depicted FIG. 6A, the bore 111 may includea predetermined region where the intensity of the magnetic fieldincreases near an end of the magnet (between the region 111 c and aregion 111 d).

Finally, the intensity of the magnetic field formed by the magnet islower in the region 111 d outside the bore 111 than inside the bore 111,and the intensity becomes lower in a direction farther from the magnetof the bore 111. Accordingly, at a location at a predetermined distancefrom the magnet of the bore 111, a magnetic field having intensity notsufficient enough for the electro-acoustic transducer 120 may bedetected.

In FIG. 6B, when the cradle 112 is moved so that the head of the patient113 is positioned at the center portion 620 of the bore 111, theelectro-acoustic transducer 120 is positioned in the region 111 b of thebore 111. That is, the electro-acoustic transducer 120 may be positionedat a position where the intensity of the magnetic field is the strongestwithin the bore 111. The controller 130 may control the intensity of aninput current so that an acoustic signal generated from theelectro-acoustic transducer 120 has a predetermined intensity (not to betoo loud or weak) by using the intensity of the magnetic field of theregion 111 b. The controller 130 may control the intensity of the inputcurrent by using the intensity of the magnetic field in the region 111 bstored in advance in the storage 131. As described above with referenceto FIG. 2, the storage 131 may store in advance information about theexperimentally obtained intensity of the magnetic field and theintensity of an input current.

In FIG. 6C, when the cradle 112 is moved so that the waist of thepatient 113 is positioned at the center portion 620 of the bore 111, theelectro-acoustic transducer 120 is positioned in region 111 c of thebore 111. That is, the electro-acoustic transducer 120 of the MRIapparatus 110 is moved inside the bore 111 further than the positionshown in FIG. 6B. As the electro-acoustic transducer 120 is moved, theintensity of the magnetic field at a point (for example, the region 111c in FIG. 6A) where the electro-acoustic transducer 120 is positioned ischanged. Accordingly, the controller 130 may control the intensity ofthe input current so that electro-acoustic transducer 120 generates anacoustic signal having the same intensity as the acoustic signalgenerated at the position in FIG. 6B.

For example, as described with reference to of FIG. 6A, since theintensity of the magnetic field varies according to the position in thebore 111, the electro-acoustic transducer 120 at the position in FIG. 6Cis affected in a smaller degree than at the position in FIG. 6B, by theintensity of the magnetic field. Therefore, the controller 130 maycontrol to increase an input current in order to generate a constantintensity acoustic signal although the intensity of the externalmagnetic field is changed.

In FIG. 6D, when the cradle 112 is moved so that the knees of thepatient 113 are positioned at the center portion 620 of the bore 111,the electro-acoustic transducer 120 is positioned in the region 111 doutside of the bore 111. The controller 130 may control to increase aninput current to the electro-acoustic transducer 120 as theelectro-acoustic transducer 120 is moved further than the position shownin FIG. 6C. That is, the controller 130 may control the intensity of theinput current according to the intensity of the magnetic field in theregion 111 d where the electro-acoustic transducer 120 is positioned.

In FIGS. 6B through 6D, the imaging process is described sequentially,with respect to the regions of the patient, but an exemplary embodimentis not limited thereto. The imaging sequence of the patient 113 is notlimited to the order of head-waist-knees. The controller 130 may controlthe intensity of the input current by using information about therelationship between the horizontal position and the intensity of inputcurrent stored in advance whenever the horizontal position of theelectro-acoustic transducer 120 changes.

The same descriptions made above with reference to FIGS. 6B through 6Din relation to the electro-acoustic transducer 120 may apply to theacoustic output device 126 that includes the electro-acoustic transducer120 described with reference to FIG. 3 (or that includes theelectro-acoustic transducer 120 and the controller 130).

According to an exemplary embodiment, the controller 130 may control theintensity of the current input to the electro-acoustic transducer 120 bydetecting a moving distance of the cradle 112 into the magnetic field.That is, the controller 130 may use the moving distance of the cradle112 in order to detect the horizontal position of the electro-acoustictransducer 120.

Also, as another example, the controller 130 may detect the horizontalposition of the electro-acoustic transducer 120 by using the intensityof the magnetic field detected by the detector 132 at a predeterminedlocation. That is, when the detector 132 provided in the acoustic outputdevice 126, the detector 132 may detect the intensity of the magneticfield that varies according to the movement of the cradle 112.Accordingly, the controller 130 may control the intensity of theacoustic signal by controlling the intensity of the current input to theelectro-acoustic transducer 120 in response to the intensity of thevarying magnetic field.

According to an exemplary embodiment, as described with reference toFIG. 2, the controller 130 may block the input current by controllingthe intensity of the input current. That is, the controller 130 maycontrol the electro-acoustic transducer 120 not to generate an acousticsignal by blocking the current input to the electro-acoustic transducer120. According to an exemplary embodiment, since the electro-acoustictransducer 120 is operated according to the magnetic field around theelectro-acoustic transducer 120, the durability of the electro-acoustictransducer 120 may be improved.

That is, the cradle 112 may be moved to a position where the intensityof the magnetic field of the electro-acoustic transducer 120 at ahorizontal position is not strong enough for the electro-acoustictransducer 120 to generate an acoustic signal. The controller 130 mayblock a current from being input to the electro-acoustic transducer 120when the horizontal position of the electro-acoustic transducer 120outside the range of a horizontal position determined in advance (therange of the horizontal position that is sufficient enough to generatean acoustic signal).

The controller 130 may block an input current based not only on thehorizontal position of the electro-acoustic transducer 120 but also onthe intensity of a magnetic field that is below a critical value. Thatis, when the detector 132 together with the electro-acoustic transducer120 is provided on the acoustic output device 126 such as a headset, thecontroller 130 may block the input current if the intensity of themagnetic field detected at the position of the headset falls below acritical value. According to an exemplary embodiment, when the headsetis not worn by the patient 113 but is kept at a separated location, thecontroller 130 may block the input current based on the intensity of themagnetic field, thereby increasing the durability of theelectro-acoustic transducer 120.

FIGS. 7A and 7B show an acoustic output device 710 according to anexemplary embodiment.

In FIG. 7A, the electro-acoustic transducer 120 is provided in a headsetas the acoustic output device 710. As depicted in FIG. 7A, theelectro-acoustic transducer 120 may generate an acoustic signal by usinga magnetic field generated in a vertical direction 708 of the MRIapparatus 110. That is, the acoustic output device 710 may include theelectro-acoustic transducer 120 that is positioned such that thevibrating direction 706 of the vibrating plate 121 or the direction ofthe central axis 123 of the coil 122 is not perpendicular to thedirection of the magnetic field of the MRI apparatus 110. The acousticoutput device 710 may include the controller 130 that controls theintensity of an input current according to the horizontal position ofthe electro-acoustic transducer 120 in the bore 111. However, anexemplary embodiment is not limited thereto, that is, the controller 130may be a separate element located outside the acoustic output device710.

FIG. 7B shows the acoustic output device 710 in which the vibratingplate 121 of the electro-acoustic transducer 120 vibrates in a direction712 perpendicular to the direction 708 of the magnetic field, accordingto an exemplary embodiment. In FIG. 7A, the vibrating plate 121 of theacoustic output device 710 vibrates, up and down, and an acoustic signal(a sound wave) generated in the acoustic output device 710 istransmitted to the patient 113 by being reflected by a side surface ofthe acoustic output device 710.

However, in the acoustic output device 710 in FIG. 7B, the vibratingplate 121 vibrates left and right laterally. That is, the acousticoutput device 710 depicted in FIG. 7B, according to an exemplaryembodiment may include a direction conversion unit 720 that is combinedwith the vibrating plate 121 to vibrate the vibrating plate 121 in adirection perpendicular to a direction of the magnetic field generatedby the coil 122 (that is, a direction of the magnetic field of the MRIapparatus 110).

According to an exemplary embodiment, an acoustic signal generated fromthe acoustic output device 710 is not transmitted by reflection but isdirectly transmitted to the patient 113. Therefore, the acoustic signalmay have a better sound quality.

FIGS. 8A, 8B, and 8C show positioning of the electro-acoustic transducer120 according to an exemplary embodiment. FIG. 8A shows theelectro-acoustic transducer 120 mounted on a head RF coil 810 accordingto an exemplary embodiment. FIGS. 8B and FIG. 8C respectively show theelectro-acoustic transducer 120 positioned on a head portion 96 of thecradle 112, according to an exemplary embodiment.

In FIG. 8A, the electro-acoustic transducer 120 may be positioned atvarious locations such as on an inner sidewall 811 a, an outer sidewall811 b, and end surface 811 c of the head RF coil 810. As describedabove, the electro-acoustic transducer 120 may be positioned so that thevibrating direction of the vibrating plate 121 or the direction of thecentral axis 123 of the coil 122 is not perpendicular to the directionof the magnetic field of the MRI apparatus 110.

The electro-acoustic transducer 120 provided at each position of thehead RF coil 810, may control the direction of transmitting an acousticsignal to the patient 113 by using the direction conversion unit 720, asdescribed with reference to FIG. 7B.

In FIGS. 8B and 8C, the electro-acoustic transducer 120 may bepositioned in a head portion 96 of the cradle 112 where the patient 113is positioned. That is, the electro-acoustic transducer 120 may beprovided at a predetermined position (that is, in the head portion 96)near the head of the patient 113 so that an acoustic signal iseffectively transmitted to patient 113 lying on the cradle 112.

As depicted in FIG. 8B, the electro-acoustic transducer 120 may bepositioned on both sides 821 a of the cradle 112 or on an upper side 821b of the cradle 112. Also, as depicted in FIG. 8C, the electro-acoustictransducer 120 may generate an acoustic signal to be transmitted to thepatient 113 by being positioned on a side 831 of the head portion 96 ofthe cradle 112.

In of FIGS. 8A through 8C, examples of positions of the electro-acoustictransducer 120 are shown. However, the MRI acoustic system 100 mayinclude the electro-acoustic transducer 120 located at various positionsand operated by various methods besides the positions and methodsdepicted and described above.

FIGS. 9A and 9B show the structure of an electro-acoustic transducer 120that includes a shield coil 900 according to an exemplary embodiment.The electro-acoustic transducer 120 depicted in FIGS. 9A and 9B includesa magnet of an MRI apparatus 110, a coil 122 through which a currentthat generates an attractive force or a repulsive force flows, avibrating plate 121 that is combined with the coil 122 to vibrateaccording to a force interacting with the MRI apparatus 110, and theshield coil 900 that shields the magnetic field generated by the coil122.

Although not shown in FIGS. 9A and 9B, the electro-acoustic transducer120 according to an exemplary embodiment may further include elements,such as a damper that supports a vertical movement of the coil 122 andthe vibrating plate 121, a bobbin combined with the coil 122, and a leadwire that connects the coil 122 to an electrical signal input terminal.

Hereinafter, the shield coil 900 depicted in FIGS. 9A and 9B will bedescribed in detail. As described with reference to FIG. 4, when acurrent flows through the coil 122 of the electro-acoustic transducer120, a magnetic field is generated. A magnetic field (different from themagnetic field in the bore 111) generated by a current that flowsthrough the coil 122 of the electro-acoustic transducer 120 is focusedon the center portion of the coil 122. A magnetic field generated by acurrent that flows through the coil 122 is smaller than that of the bore111 of the MRI apparatus 110, but may affect a main magnetic field ofthe MRI apparatus 110 for obtaining an MRI image. Accordingly, there isa need to offset or minimize a magnetic field generated by a currentthat flows in the coil 122.

The shield coil 900 depicted in FIGS. 9A and 9B has the same centralaxis as the central axis 123 of the coil 122, and may be positionedinside or outside the coil 122. In FIG. 9A, as an example, the shieldcoil 900 is positioned outside the coil 122, and in FIG. 9B, the shieldcoil 900 is positioned inside the coil 122. In FIGS. 9A and 9B, thethicknesses of the coil 122 and the shield coil 900 are different fromeach other for convenience of explanation and understanding.Nevertheless, the thicknesses of the coil 122 and the shield coil 900may be the same or different.

The direction of a current (hereinafter, a second current) that flowsthrough the shield coil 900 and the direction of a current (hereinaftera first current) that flows through the coil 122 are opposite to eachother. That is, the direction of a magnetic field (a direction accordingto the Ampere's Rule (the Right Hand Screw Rule)) generated by theshield coil 900 is opposite to the direction of a magnetic fieldgenerated by the coil 122, and thus, the magnetic field focused on thecenter portion of the coil 122 may be offset by the magnetic fieldgenerated by the shield coil 900.

According to an exemplary embodiment, the intensities of the first andsecond currents may be controlled by the controller 130. That is, thecontroller 130 may control the intensity of the first current to bedifferent from that of the second current when controlling the intensityof a current input to the electro-acoustic transducer 120.

More specifically, the shield coil 900 depicted in FIG. 9A has a lengthgreater than the coil 122, and thus, if the intensities of the firstcurrent and the second current are equal, the intensity of a magneticfield generated by the shield coil 900 is greater than that of themagnetic field generated by the coil 122. Accordingly, the controller130 may control the intensity of the second current that flows throughthe shield coil 900 to be smaller than that of the first current thatflows through the coil 122 so that the intensities of the magneticfields generated by the shield coil 900 and the coil 122 are equal.

On the contrary, the shield coil 900 depicted in FIG. 9B has a lengthsmaller than that of the coil 122. Accordingly, the controller 130 maycontrol the intensity of the first current that flows through the coil122 to be smaller than that of the second current that flows through theshield coil 900 by controlling the intensity of the current input to theelectro-acoustic transducer 120.

The magnetic field generated by the coil 122 may be offset or minimizedby controlling the numbers of turns of the coil 122 and the shield coil900. That is, for example, in FIG. 9A, the intensity of the magneticfield generated by the coil 122 may be increased by winding the coil 122by a greater number of turns than the shield coil 900. In this way, themagnetic field may be offset by controlling the numbers of windings ofthe shield coil 900 and the coil 122.

FIGS. 10A and 10B show the electro-acoustic transducer 120 that includesfixing units 1010 and 1020 according to an exemplary embodiment. InFIGS. 10A and 10B, the shield coil 900 is connected to the fixing units1010 and 1020.

The fixing units 1010 and 1020 depicted in of FIGS. 10A and 10B fix theshield coil 900 by being connected thereto. That is, the fixing units1010 and 1020 may fix the shield coil 900 so that the shield coil 900does not generate an attractive force or a repulsive force with themagnet of the MRI apparatus 110. If the shield coil 900 is not fixed,the shield coil 900 may move by a force interacting with the magnet ofthe MRI apparatus 110, and thus, noise may be included in an acousticsignal generated by the coil 122 combined with the vibrating plate 121.Although not shown in FIGS. 10A and 10B, the fixing units 1010 and 1020may fix the shield coil 900 by being combined with a frame of theelectro-acoustic transducer 120.

The fixing unit 1010 depicted in FIG. 10A may fix the shield coil 900 bybeing combined with the shield coil 900 that is located outside the coil122. On the contrary, the fixing unit 1020 depicted in FIG. 10B fix theshield coil 900 by being combined with the shield coil 900 locatedinside the coil 122. The fixing units 1010 and 1020 shown in FIGS. 10Aand 10B are only examples to fix the shield coil 900, and thus, theshield coil 900 may be fixed on the frame of the electro-acoustictransducer 120 through various methods, for example, by using an elasticmember such as a spring.

FIG. 11 is a perspective view showing the structure of a case typeelectro-acoustic transducer 1100 according to an exemplary embodiment.In FIG. 11, the electro-acoustic transducer 1100 is of a different typefrom the electro-acoustic transducer 120 described above.

The electro-acoustic transducer 1100 may include a vibrating unit 1110that vibrates according to a Lorentz force formed by an MRI apparatus110, a supporting unit 1130 that fixes both edges of the vibrating unit1110, and a coil through which a current that experiences the Lorentzforce flows. The structure of the electro-acoustic transducer 1100depicted in FIG. 11 is an example, and thus, the electro-acoustictransducer 1100 that includes the vibrating unit 1110, the supportingunit 1130, and the coil may further include structure besides thestructure depicted in FIG. 11.

The coil through which a current flows in the electro-acoustictransducer 1100 depicted in FIG. 11 may include at least one first coil1120 disposed on the vibrating unit 1110 and at least one second coil1140 fixed on the supporting unit 1130. That is, when a current is inputthrough an input terminal 1150 depicted in FIG. 11, the current may flowthrough the first coil on the vibrating unit 1110, and may flow throughthe second coil 1140 fixed on the supporting unit 1130 at one end of thevibrating unit 1110. Next, the current that flows through the secondcoil 1140 that is fixed on the supporting unit 1130 flows along a lowerend surface of the electro-acoustic transducer 1100, and may flow againthrough the first coil 1120 at the other end of the vibrating unit 1110.

Also, according to the electro-acoustic transducer 1100 depicted in FIG.11, the first coil 1120 and the second coil 1140 are parallel to eachother, and the current flows therethrough in opposite directions to eachother. That is, since the current flows continuously through the firstcoil 1120 and the second coil 1140, the direction of the current thatflows in the vibrating unit 1110 and the direction of the current thatflows in the lower end surface of the supporting unit 1130 are oppositeto each other. According to the structure described above, a magneticfield outside an ideal solenoid coil is 0, and thus, a magnetic fieldgenerated outside the electro-acoustic transducer 1100 depicted in FIG.11 may be minimized.

In the structure of the electro-acoustic transducer 1100 according to anexemplary embodiment, the effect of a magnetic field generated by acurrent that flows through the coil of the electro-acoustic transducer1100 to a magnetic field of the MRI apparatus 110 may be minimized.

The vibrating unit 1110 of the electro-acoustic transducer 1100 may berealized in various ways. That is, the vibrating unit 1110 may include afilm type vibrating plate or an elastic member vibrating plate. Inaddition, the vibrating unit 1110 may be realized in variousconfigurations that may vibrate according to the Lorentz force.

When the electro-acoustic transducer 1100 according to an exemplaryembodiment operates, the vibrating unit 1110 and the first coil 1120vibrate according to the Lorentz force, but the second coil 1140 isfixed on the supporting unit 1130. Accordingly, the first coil 1120 andthe second coil 1140 of the electro-acoustic transducer 1100 may beseparately attached to or formed on the vibrating unit 1110 and thesupporting unit 1130. That is, each of the first coil 1120 and thesecond coil 1140 may be combined after being formed as separate parts.

For example, the first coil 1120 disposed in advance on the vibratingunit 1110 and the second coil 1140 fixed on the supporting unit 1130 maybe connected by a well-known suitable technique in the art, such asbonding or assembling the vibrating unit 1110 and the supporting unit1130. Accordingly, the combined first coil 1120 and the second coil 1140may form a coil that surrounds the vibrating unit 1110 and thesupporting unit 1130 of the electro-acoustic transducer 1100.

However, the electro-acoustic transducer 1100 may be formed by disposinga single coil along a surface of the supporting unit 1130 and thevibrating unit 1110 that are combined in advance. That is, the coil ofthe electro-acoustic transducer 1100 is not combined after the firstcoil 1120 and the second coil 1140 are separately formed, but in a coilformed in advance, parts that are connected to the vibrating unit 1110and the supporting unit 1130 respectively may be the first coil 1120 andthe second coil 1140.

Hereinafter, a process of operating the electro-acoustic transducer 1100depicted in FIG. 11 according to a Lorentz force will be described. Acurrent that flows in a magnetic field receives the Lorentz force, andthe direction of the Lorentz force is perpendicular to the direction ofthe magnetic field according to the Fleming's left-hand rule.

In FIG. 11, a direction of a magnetic field is indicated by “B”. When acurrent flows in the direction indicated by “B”, the electro-acoustictransducer 1100 that uses a magnetic field of the MRI apparatus 110receives a Lorentz force (indicated by “F”) in an upper direction, whichis perpendicular to the vibrating unit 1110. The vibrating unit 1110vibrates according to the Lorentz force, and a sound wave generated bythe vibration of the vibrating unit 1110 may generate an acousticsignal.

The vibrating unit 1110 may be formed of a nonmagnetic material.According to an exemplary embodiment, the vibrating unit 1110 may beformed of a paramagnet material or a low magnetic material that affectsa magnetic field of the MRI apparatus 110 less than a critical value.

When an alternating (AC) current is input to the electro-acoustictransducer 1100, the direction of the Lorentz force that is received bythe vibrating unit 1110 varies together with the direction of thecurrent that varies as the direction of the magnetic field ismaintained. That is, when a current flows in the direction depicted inFIG. 11, the direction of the Lorentz force is upward, which isperpendicular to the vibrating unit 1110. However, when the currentflows in a counter direction, the direction of the Lorentz is downward,which perpendicular to the vibrating unit 1110. The vibrating unit 1110vibrates according to the Lorentz force and may generate an acousticsignal.

As described above, the electro-acoustic transducer 1100 depicted inFIG. 11 according to an exemplary embodiment may be positioned so thatthe vibrating unit 1110 is parallel to the direction of a magnet of theMRI apparatus 110 and the current that flows through the first coil 1120disposed on the vibrating unit 1110 is perpendicular to the direction ofthe magnetic field. That is, the electro-acoustic transducer 1100 may bepositioned in a direction that the current that flows through the firstcoil 1120 experiences the Lorentz force generated by a magnetic field ofthe MRI apparatus 110.

The electro-acoustic transducer 1100 receives the Lorentz force the mostwhen a direction of the current is perpendicular to the direction of amagnet field. However, an angle that is formed by the two directionsaccording to the current invention is not limited to 90°. That is, theLorentz force that is transmitted to the electro-acoustic transducer1100 from the magnetic field of the MRI apparatus 110 is generated whenan angle between the direction of the current and the direction of themagnetic field is not 0° or 180°. Accordingly, the electro-acoustictransducer 1100 may be positioned so that the direction of the currentand the direction of the magnetic field are not parallel to each other.

The supporting unit 1130 of the electro-acoustic transducer 1100 mayinclude at least one aperture 1160. The aperture 1160 formed in thesupporting unit 1130 may form a path through which an air in theelectro-acoustic transducer 1100 is circulated as the vibrating unit1110 vibrates. In FIG. 11, the aperture 1160 is formed in a bottom ofthe supporting unit 1130 in a rectangular shape. However, the shape andlocation of the aperture 1160 according to an exemplary embodiment isnot limited thereto. That is, the aperture 1160 may have various shapes,and may be formed not only in the bottom of the supporting unit 1130 butalso in a sidewall (that is, a sidewall of the supporting unit 1130where the coil is not formed) of the supporting unit 1130.

According to an exemplary embodiment described above, theelectro-acoustic transducer 1100 that includes the vibrating unit 1110and the supporting unit 1130 may vibrate according to the Lorentz forcethat is generated when a current flows through the coil 1120, and thus,may generate an acoustic signal. The electro-acoustic transducer 1100described above is one case selected for convenience of explanation, andthus, the vibrating unit 1110, the supporting unit 1130, and the coilmay be of various types.

FIG. 12A is a lateral view showing a structure of the electro-acoustictransducer 1200 according to an exemplary embodiment. Theelectro-acoustic transducer 1200 depicted in FIG. 12A is a lateral viewof the electro-acoustic transducer 1100 described with reference to FIG.11, and thus, overlapping descriptions are omitted.

As depicted in FIG. 12A, the electro-acoustic transducer 1200 includesthe first coil 1120 formed on the vibrating unit 1210. The first coil1120 is disposed on the vibrating unit 1210, vibrates together with thevibrating unit 1210 according to the Lorentz force, and is combined withthe second coil 1140 so that a current that generate the Lorentz forceflows therethrough.

The first coil 1120 according to an exemplary embodiment may include athin-film coil formed through gilding by printing a predeterminedpattern on an insulating film, or formed by etching a copper foil thatis bonded to an insulating film.

When the first coil 1120 and the second coil 1140 are formed as one coiland are fixed on the vibrating unit 1210 and the supporting unit 1130,the second coil 1140 may include a thin-film coil like the first coil1120. However, when the first coil 1120 and the second coil 1140 areformed separately and are combined with each other, the second coil 1140may be formed through a process different from that of the first coil1120 and may be disposed on the supporting unit 1130.

FIG. 12B is a lateral view of the structure of the electro-acoustictransducer 1200 according to an exemplary embodiment. Unlike theelectro-acoustic transducer 1100 depicted FIG. 12A, the electro-acoustictransducer 1200 depicted of FIG. 12B may include two vibrating units,that is, a first vibrating unit 1210 and a second vibrating unit 1220disposed parallel to each other. Both edges of the first vibrating unit1210 and the second vibrating unit 1220 of the electro-acoustictransducer 1200 depicted in FIG. 12A are respectively combined with thesupporting unit 1130.

The first coils 1120 may be respectively disposed on the first vibratingunit 1210 and the second vibrating unit 1220. The description of thefirst vibrating unit 1210 is the same as the descriptions made withreference to FIG. 11 and FIG. 12A, and the first coil 1120 may also bedisposed on the second vibrating unit 1220 (on a surface facing outsidethe electro-acoustic transducer 1200). The first coils 1120 disposed onthe first vibrating unit 1210 and the second vibrating unit 1220 areconnected to the second coil 1140 provided on the supporting unit 1130to receive the Lorentz force while a current flows therethrough.

According to an exemplary embodiment, in the electro-acoustic transducer1200 depicted FIG. 12B, when the first vibrating unit 1210 vibrates inan upward direction, the second vibrating unit 1220 vibrates in adownward direction, that is, the first vibrating unit 1210 and thesecond vibrating unit 1220 may generate an acoustic signal having thesame phase by vibrating in opposite directions. In the electro-acoustictransducer 1200 according to an exemplary embodiment depicted in FIG.12B, apertures may be formed in a side surface of the supporting unit1130.

FIG. 13 is a perspective view showing a structure of an electro-acoustictransducer 1250 according to an exemplary embodiment. Theelectro-acoustic transducer 1250 depicted in FIG. 13 includes avibrating unit 1110, a first coil 1120, and a supporting unit 1130. Thatis, the electro-acoustic transducer 1250 depicted in FIG. 13 has astructure that does not include the second coil 1140 fixed on thesupporting unit 1130.

The electro-acoustic transducer 1250 is operated as similarly to theoperation described with reference to FIG. 11. That is, a current thatflows in a direction indicated by arrows in the first coil 1120 receivesthe Lorentz force in a direction indicated by “F” in a magnetic field ina direction indicated by “B” in FIG. 13. Accordingly, the vibrating unit1110 on which the first coil 1120 is disposed vibrates according to theLorentz force and generates an acoustic signal. At least both edges ofthe vibrating unit 1110 are fixed by combining them with the supportingunit 1130.

The first coil 1120 is disposed on the vibrating unit 1110 by forming atleast one repeating pattern. That is, as depicted in FIG. 13, the firstcoil 1120 may be disposed by forming a repeating pattern having arectangular shape.

According to an exemplary embodiment, several of the first coils 1120may be disposed so that the position of the center portion of therepeating pattern is biased on a side of the first coils 1120. That is,in FIG. 13 as an example, the first coils 1120 may be disposed toreceive the Lorentz force in the same direction by disposing someportions of the first coils 1120 that coincide with the direction of acurrent (the direction of the arrows indicated along the first coils1120) on the vibrating unit 1110. In other words, a portion of the firstcoils 1120 through which a current flow in a predetermined direction maybe disposed to be located on a predetermined region (for example, on acentral region) of the vibrating unit 1110.

A portion of the first coils 1120 besides the portion indicated byarrows in FIG. 13, that is, a portion of the first coils 1120 throughwhich a current flows in a direction in which a force indicated by “F”is not received may be located in an outer region of the vibrating unit1110. Accordingly, the first coils 1120 that are disposed in an outerregion of the vibrating unit 1110 may be disposed on a portion of thevibrating unit 1110 that is fixed on the supporting unit 1130. As aresult, the first coils that receive the Lorentz force in a constantdirection according to the vibrating unit 1110 may generate an acousticsignal by vibrating in the same direction.

FIG. 14 is a perspective view showing a structure of an electro-acoustictransducer 1250 according to an exemplary embodiment. Theelectro-acoustic transducer 1250 of FIG. 14 includes a plurality ofpatterns.

That is, in the vibrating unit 1110 of the electro-acoustic transducer1250 of FIG. 14, the first coils 1120 may be disposed so that therepeated pattern depicted in FIG. 13 is consecutively formed. In thefour repeated patterns depicted in FIG. 14, the location of the centerof each of the repeated patterns is biased on a side of the first coils1120.

That is, the first coils 1120 may be disposed such that, a portion ofthe first coils 1120 through which a current does not flow in adirection indicated by arrows is disposed to be located on a region ofthe vibrating unit 1110 that is not fixed, and a portion of the firstcoils 1120 through which the current flows in a direction besides thedirection indicated by the arrows is disposed to be located on a regionof the vibrating unit 1110 that is fixed on the supporting unit 1130.According to an exemplary embodiment, the vibrating unit 1110 of theelectro-acoustic transducer 1250 may generate an acoustic signal byvibrating in the same direction by being located on a portion of thefirst coils 1120 where a current flows in a constant direction.

FIGS. 15A and 15B show the structure of an electro-acoustic transducer1280 according to an exemplary embodiment. The electro-acoustictransducer 1280 depicted in FIG. 15 has a structure in which thevibrating unit 1110 includes a vibrating plate and a connection unit1125 connects the vibrating unit 1110 to the supporting unit 1130.

FIG. 15A is a plan view of the electro-acoustic transducer 1280according to an exemplary embodiment, and a shadow region indicates aregion where the vibrating unit 1110 is separated from the supportingunit 1130. That is, the vibrating unit 1110 includes a vibrating plateformed of an elastic member, and is connected to the supporting unit1130 by being combined with the flexible connection unit 1125. FIG. 15Bis a lateral view of the electro-acoustic transducer 1280 according toan exemplary embodiment, and shows a configuration of connecting thevibrating unit 1110 to the supporting unit 1130 by the connection unit1125. In FIG. 15B, the first coil 1120 is disposed on or proximate alower surface 1132 of the vibrating unit 1110. However, the location ofthe first coil 1120 is not limited thereto.

In the electro-acoustic transducer 1280 depicted in FIG. 15, theelectro-acoustic transducer 1280 is located in a magnetic field, andwhen a current flows through the first coil 1120, the Lorentz force isreceived in a direction indicated by “F”. Accordingly, the vibratingunit 1110 vibrates while being connected to the connection unit 1125,and thus, may generate an acoustic signal.

FIGS. 16A and 16B show positioning of the case type electro-acoustictransducer 1100 according to an exemplary embodiment in the bore 111 ofthe MRI apparatus 110. FIG. 16A is a lateral view of the bore 111, andFIG. 16B is a front or rear view of the bore 111.

In FIG. 16A, the electro-acoustic transducer 1100 may be positioned sothat the direction 30 of the magnetic field generated by the magnet ofthe MRI apparatus 110 and the direction of the current flow are notparallel to each other. That is, as depicted in FIG. 16A, theelectro-acoustic transducer 1100 may be positioned on a side of the bore111 so that the direction of the magnetic field and the direction of thecurrent are not parallel to each other. That is, an angle that is formedby the two directions may be greater than 0° and less than 90°.

In two electro-acoustic transducers 1100 depicted in FIG. 16A, a greyregion indicates the electro-acoustic transducer 1100 that is positionedso that the vibrating unit 1110 faces an inner side of the bore 111.

In FIG. 16B, the electro-acoustic transducer 1100 generates an acousticsignal by being positioned in an upper area and both side areas of thebore 111. That is, to transmit the acoustic signal to the patient 113positioned on the cradle 112, the electro-acoustic transducer 1100 maybe positioned so that the vibrating unit 1110 vibrates in a directiontowards the patient 113. As shown in FIG. 16A, the electro-acoustictransducer 1100 may generate an acoustic signal when the direction ofthe magnetic field and the direction of the current are not parallel toeach other. The generation of the acoustic signal may be very effectivewhen the electro-acoustic transducer 1100 is positioned so that twodirections are perpendicular to each other.

FIG. 17 is a drawing showing mounting of the electro-acoustic transducer1100 in an acoustic output device 1190 according to an exemplaryembodiment. In FIG. 17, the electro-acoustic transducer 1100 may bemounted on the acoustic output device 1190 so that the direction of acurrent that flows in the first coil 1120 located on the vibrating unit1110 is not parallel to the direction 30 of a magnetic field.

According to an exemplary embodiment, the electro-acoustic transducer1100 may be mounted on the acoustic output device 1190 such as aheadset, and an acoustic signal generated from the electro-acoustictransducer 1100 may be directly transmitted to the patient 113.

FIG. 18A is a perspective view showing positioning of theelectro-acoustic transducer 1100 on a head RF coil 810 according to anexemplary embodiment. The electro-acoustic transducer 1100 according toan exemplary embodiment, as depicted in FIG. 18A, may be positioned onan inner side surface 812 or an outer side surface 814 of the head RFcoil 810. When the electro-acoustic transducer 1100 is positioned on theinner side surface of the head RF coil 810, the electro-acoustictransducer 1100 may generate an acoustic signal in a direction towardsthe patient 113.

A dark region is a rear surface of the electro-acoustic transducer 1100.According to an exemplary embodiment, the electro-acoustic transducer1100 positioned in the head RF coil 810 may be positioned to face thepatient 113 as depicted in FIG. 16A, and also, may output an acousticsignal outwards of the head RF coil 810 by being positioned in adirection opposite to the patient 113.

FIG. 18B is a perspective view showing positioning of theelectro-acoustic transducer 1100 on the cradle 112. The electro-acoustictransducer 1100 according to an exemplary embodiment may transmit anacoustic signal to the patient 113 by being positioned at a head portion96 of the cradle 112. The electro-acoustic transducer 1100 mounted onthe head portion 96 may be positioned so that the direction of a currentflow is not parallel to the direction of a magnetic field.

FIGS. 19A, 19B, and 19C show a pattern of an electro-acoustic transducer1300 according to an exemplary embodiment. The electro-acoustictransducer 1300 according to an exemplary embodiment may include avibrating unit 1310, 1320, and 1330, respectively, and a coil that isdisposed on the vibrating unit 1310, 1320, and 1330 and through which acurrent flows. FIGS. 19A, 19B, and 19C respectively show variouspatterns 1311, 1321, and 1331 formed on the vibrating units 1310, 1320,and 1330 of the electro-acoustic transducer 1300. The vibrating units1310, 1320, and 1330 may be formed of a non-magnetic material or afeeble magnetic material, and as described above, may include avibrating film or a vibrating plate.

In FIGS. 19A, 19B, and 19C, solid lines indicate coils through which acurrent flows on the vibrating units 1310, 1320, and 1330, and dottedlines indicate coils through which a current flows on lower surfaces ofthe vibrating units 1310, 1320, and 1330.

The electro-acoustic transducer 1300 according to an exemplaryembodiment may include a first coil that includes at least one repeatingpattern and through which a current that generates an attractive forceor a repulsive force with respect to a magnetic field of the MRIapparatus 110 flows and a second coil through which the same currentthat is input to the first coil flows. That is, in FIGS. 19A, 19B, and19C, the parts shown by solid lines may be first coils, and the partsshown by dotted lines may be second coils. However, as described above,since the second coil is a coil through which the same current input tothe first coil and the current output from the first coil flows, thefirst and second coils are not limited to the coils indicated by thesolid lines and the dotted lines as depicted above.

For example, the second coil, through which the current input to thefirst coil and the current output from the first coil flow, may includenot only the parts shown by dotted lines on lower surfaces of thevibrating units 1310, 1320, and 1330 in FIGS. 19A, 19B, and 19C, butalso the parts shown by solid lines from an input terminal indicated by“+” to a point where the first pattern of at least one of the repeatingpatterns begins. For example, in FIG. 19B, the second coil may includenot only the parts shown by dotted lines, but also the parts besides thescrew pattern parts of the coil. The second coil may include all coilsbesides at least one repeating pattern disposed on the lower surfaces ofthe vibrating units 1310, 1320, and 1330.

The electro-acoustic transducer 1300 depicted in FIGS. 19A, 19B, and 19Cmay be positioned in the magnetic field of the MRI apparatus 110 so thatthe magnetic field of the MRI apparatus 110 is perpendicular (in FIG.19A, a vertical upward direction) to the vibrating units 1310, 1320, and1330. When a current is input to the first coil of the electro-acoustictransducer 1300, the first coil generates a magnetic field having aconstant direction (the Ampere's right-handed screw rule direction).That is, when a current flows in the first coil in a direction indicatedby the arrow, the direction of the magnetic field that is generated bythe first coil is a downward direction (in a direction opposite to themagnetic field of the MRI apparatus 110) perpendicular to the vibratingunits 1310, 1320, and 1330.

As described above, when an AC current is input to the electro-acoustictransducer 1300, the direction of the current varies every moment, andaccordingly, the vibrating units 1310, 1320, and 1330 generate magneticfields having the same direction as or opposite direction to themagnetic field of the MRI apparatus 110. Accordingly, the vibratingunits 1310, 1320, and 1330 may generate an acoustic signal by vibratingdue to an attractive force or a repulsive force of the MRI apparatus110.

The first coil disposed on the vibrating units 1310, 1320, and 1330 mayform at least one pattern 1311, 1321, and 1331 by consecutively beingdisposed in a predetermined direction. That is, as depicted in FIGS.19A, 19B, and 19C, the coil may be disposed on the vibrating units 1310,1320, and 1330 by being wound in a predetermined clock direction. Thus,the coil may generate a uniform magnetic field in a predetermineddirection (Ampere's right-handed screw rule direction) when a currentflows therethrough.

In FIGS. 19A, 19B, and 19C, the first coils form rectangular shapepatterns 1311 and 1331 on the vibrating units 1310 and 1330, and in FIG.19B, the first coil forms a screw shape pattern on the vibrating unit1320. As described above, at least one repeating pattern of the firstcoil may be formed on the vibrating units 1310, 1320, and 1330.

According to an exemplary embodiment, the electro-acoustic transducer1300 may further include a supporting unit (not shown), the supportingunit being combined with both edges or corners of the vibrating units1310, 1320, and 1330 so that the vibrating units 1310, 1320, and 1330vibrate according to a interacting force with the MRI apparatus 110. Thesupporting unit according to an exemplary embodiment may be realizedsimilarly to the supporting unit 1130 described with reference to FIG.11.

According to the MRI acoustic system, the electro-acoustic transducer,and the acoustic output device of an exemplary embodiment, an acousticsignal may be effectively transmitted to a patient located in a bore ofthe MRI apparatus by using a magnetic field of the MRI apparatus insteadof using a magnetic material to generate the acoustic signal.

Therefore, an acoustic signal in a wide frequency band may be outputwithout affecting the magnetic field of the MRI apparatus. Although theintensity of the magnetic field is changed by moving the cradle, anacoustic signal having a constant magnitude may be generated.

Also, the costs for manufacturing the MRI acoustic system may be reducedwhen compared to a piezo-electric speaker, a related art loud speaker,or a related art dynamic speaker by not using a magnetic material suchas a magnet or an iron body. Also, the durability of theelectro-acoustic transducer, the acoustic output device, and the MRIacoustic system may be increased by blocking a current input to theelectro-acoustic transducer according to the intensity of a magneticfield of the MRI apparatus or the position of the cradle.

Although a few exemplary embodiments have been shown and described, itwould be appreciated by those skilled in the art that various changes inform and detail may be made in these exemplary embodiments withoutdeparting from the spirit and scope of the disclosure, the scope ofwhich is defined by the claims and their equivalents.

What is claimed is:
 1. A magnetic resonance imaging (MRI) acousticsystem comprising: a magnet; an electro-acoustic transducer thatcomprises a coil through which a current flows so that an attractiveforce or a repulsive force is generated with respect to the magnet, anda vibrating plate that vibrates in response to the attractive force orthe repulsive force; and a controller that controls an intensity of acurrent input to the electro-acoustic transducer according to a positionof the electro-acoustic transducer in a magnetic field generated by themagnet.
 2. The MRI acoustic system of claim 1, further comprising astorage that stores in advance the intensity of the current according tothe position of the electro-acoustic transducer, wherein the controllercontrols the intensity of the current so that the vibrating platevibrates regardless of an intensity of the magnetic field according to achange of the position of the electro-acoustic transducer.
 3. The MRIacoustic system of claim 1, further comprising a detector that detectsan intensity of the magnetic field, wherein the controller blocks thecurrent from being input to the electro-acoustic transducer when theintensity of the magnetic field is below a certain value.
 4. The MRIacoustic system of claim 1, wherein the controller blocks the currentfrom being input to the electro-acoustic transducer when the position ofthe electro-acoustic transducer is outside a predetermined range.
 5. TheMRI acoustic system of claim 1, further comprising a filter thatprevents an interference between radio-frequency (RF) signals generatedby an MRI apparatus and the electro-acoustic transducer, respectively.6. The MRI acoustic system of claim 1, wherein the electro-acoustictransducer is disposed so that a vibrating direction of the vibratingplate and a direction of a magnetic flux focused by the magnet are notperpendicular to each other.
 7. The MRI acoustic system of claim 1,wherein the electro-acoustic transducer is positioned in the magneticfield formed by the magnet so that a central axis of the coil and adirection of a magnetic flux focused by the magnet are not perpendicularto each other.
 8. The MRI acoustic system of claim 1, wherein theelectro-acoustic transducer is positioned at a head portion of a cradlewhere a patient is located to be moved into the magnetic field.
 9. TheMRI acoustic system of claim 8, wherein the controller controls theintensity of the current according to a moving distance of the cradleinto the magnetic field of an MRI apparatus.
 10. The MRI acoustic systemof claim 1, wherein the electro-acoustic transducer is mounted on a headradio-frequency (RF) coil of an MRI apparatus.
 11. The MRI acousticsystem of claim 1, wherein the electro-acoustic transducer is mounted ona headset or an earphone.
 12. The MRI acoustic system of claim 1,further comprising a detector that detects the intensity of the magneticfield, wherein the controller controls the intensity of the currentaccording to the intensity of the detected magnetic field.
 13. Anacoustic output device that uses a magnetic field of a magneticresonance imaging (MRI) apparatus, the acoustic output devicecomprising: a coil through which a current for generating an attractiveforce or a repulsive force with respect to a magnet of the MRI apparatusflows; a vibrating plate that vibrates according to the attractive forceor the repulsive force; and a controller that controls an intensity of acurrent that flows in the coil according to a position of anelectro-acoustic transducer with respect to the magnetic field.
 14. Theacoustic output device of claim 13, further comprising a storage thatstores in advance intensity values of the current according to theposition of the electro-acoustic transducer, wherein the controllercontrols the intensity of the current so that the vibrating platevibrates regardless of an intensity of the magnetic field according to achange in the position of the electro-acoustic transducer.
 15. Theacoustic output device of claim 13, further comprising a detector thatdetects the intensity of the magnetic field, wherein the controllerblocks a current from being input to the electro-acoustic transducerwhen the intensity of the magnetic field is below a certain value. 16.The acoustic output device of claim 13, wherein the controller blocksthe current from being input to the electro-acoustic transducer when theposition of the electro-acoustic transducer is outside a predeterminedrange.
 17. The acoustic output device of claim 13, further comprising aheadset or an earphone.
 18. An electro-acoustic transducer that uses amagnetic field of a magnetic resonance imaging (MRI) apparatus, theelectro-acoustic transducer comprising: a first coil through which afirst current for generating an attractive force or a repulsive forcewith respect to the MRI apparatus flows; a second coil for reducing amagnetic field generated by the first current that flows in the firstcoil; and a vibrating plate that vibrates according to the attractiveforce or the repulsive force.
 19. The electro-acoustic transducer ofclaim 18, wherein a second current having a predetermined intensityflows through the second coil to reduce the magnetic field generated bythe first coil.
 20. The electro-acoustic transducer of claim 18, whereinthe second coil is wound by a predetermined number of turns for reducingthe magnetic field generated by the first coil.
 21. The electro-acoustictransducer of claim 18, further comprising a fixing unit that fixes thesecond coil, wherein the second coil has a concentric axis with thefirst coil and is combined with the fixing unit on an inner side or anouter side of the first coil.
 22. The electro-acoustic transducer ofclaim 18, wherein a direction of a second current that flows through thesecond coil is opposite to a direction of the first current that flowsthrough the first coil.
 23. The electro-acoustic transducer of claim 18,wherein the electro-acoustic transducer is positioned on a head portionof a cradle where patient is located in the MRI apparatus.
 24. Theelectro-acoustic transducer of claim 18, wherein the electro-acoustictransducer is mounted on a head radio-frequency (RF) coil of the MRIapparatus.
 25. The electro-acoustic transducer of claim 18, wherein theelectro-acoustic transducer is mounted on a headset or an earphone. 26.An acoustic system that comprises the electro-acoustic transducer ofclaim
 18. 27. An electro-acoustic transducer that uses a magnetic fieldof a magnetic resonance imaging (MRI) apparatus, the electro-acoustictransducer comprising: a vibrating unit that vibrates according to aLorentz force generated by the magnetic field; a supporting unit thatfixes both edges of the vibrating unit; and a first coil that isdisposed on the vibrating unit and vibrates together with the vibratingunit.
 28. The electro-acoustic transducer of claim 27, furthercomprising a second coil that is fixed on the supporting unit and iscombined with the first coil.
 29. The electro-acoustic transducer ofclaim 28, wherein the first coil and the second coil are disposed alongat least one surface of the supporting unit and the vibrating unit. 30.The electro-acoustic transducer of claim 28, wherein the first coil andthe second coil are parallel to each other, and currents respectivelyflow therethrough in opposite directions.
 31. The electro-acoustictransducer of claim 27, wherein the first coil comprises a thin filmcoil formed on the vibrating unit.
 32. The electro-acoustic transducerof claim 27, wherein the vibrating unit comprises a first vibrating unitand a second vibrating unit disposed in parallel to the first vibratingunit, both edges of the first vibrating unit and both edges of thesecond vibrating unit being respectively combined with the supportingunit, and the first coil is disposed on the first and second vibratingunits.
 33. The electro-acoustic transducer of claim 27, wherein thefirst coil is disposed on the vibrating unit in at least one repeatingpattern.
 34. The electro-acoustic transducer of claim 33, wherein thefirst coil is disposed so that a location of a center of the repeatingpattern is biased on a side of the first coil.
 35. The electro-acoustictransducer of claim 27, wherein the vibrating unit comprises: avibrating plate that vibrates due to the Lorentz force and is separatedfrom the supporting unit; and a connection unit that connects thevibrating plate to the supporting unit, wherein the first coil isdisposed on the vibrating plate.
 36. The electro-acoustic transducer ofclaim 27, wherein the vibrating unit comprises a vibrating film thatvibrates due to the Lorentz force.
 37. The electro-acoustic transducerof claim 27, wherein the vibrating unit comprises a vibrating plate thatvibrates due to the Lorentz force and is formed of an elastic member.38. The electro-acoustic transducer of claim 27, wherein theelectro-acoustic transducer is positioned on a head portion of a cradlewhere a patient is positioned in the MRI apparatus.
 39. Theelectro-acoustic transducer of claim 27, wherein the electro-acoustictransducer is mounted on a head radio-frequency (RF) coil of the MRIapparatus.
 40. The electro-acoustic transducer of claim 27, wherein theelectro-acoustic transducer is mounted on a headset or an earphone. 41.An MRI acoustic system comprising the electro-acoustic transducer ofclaim
 27. 42. An electro-acoustic transducer that uses a magnetic fieldof a magnetic resonance imaging (MRI) apparatus, the electro-acoustictransducer comprising: a vibrating unit that vibrates according to anattractive force or a repulsive force with respect to a magnet of theMRI apparatus; a first coil that is disposed on the vibrating unit in arepeating pattern and through which a current for generating theattractive force or the repulsive force flows; and a second coil that iscombined with the first coil, and through which a current input to thefirst coil and output from the first coil flows.
 43. Theelectro-acoustic transducer of claim 42, wherein the repeating patterncomprises a screw shape pattern.
 44. The electro-acoustic transducer ofclaim 42, wherein the repeating pattern comprises a rectangular shapepattern.
 45. The electro-acoustic transducer of claim 42, wherein thefirst coil comprises patterns that are formed by consecutively disposingthe patterns along a predetermined direction on the vibrating unit. 46.The electro-acoustic transducer of claim 42, wherein the second coil isdisposed on a lower surface of the vibrating unit.
 47. An MRI acousticsystem comprising the electro-acoustic transducer of claim 42.